Assertion (A): Chlorophyll usually show red fluorescence though they absorb blue radiations as well. Reason (R) : In fluorescence, long wave radiations are emitted.

Assertion (A) is true because chlorophyll molecules strongly absorb light in both the blue (around 430 nm) and red (around 660 nm) regions of the spectrum [t2, t5]. However, regardless of whether blue or red light is absorbed, the resulting fluorescence is typically red. This occurs because the excited electrons quickly lose energy through non-radiative relaxation to the lowest excited state before emitting a photon. Reason (R) is also true and provides the correct explanation via the principle of fluorescence and the Stokes shift. In fluorescence, the emitted radiation always has a longer wavelength (lower energy) than the absorbed radiation [t4, t8]. Since blue light has a shorter wavelength than red light [c4], the energy absorbed from blue light is emitted at the longer red wavelength, resulting in the characteristic red fluorescence of chlorophyll [t1, t4].

Sources

1. [1] https://pmc.ncbi.nlm.nih.gov/articles/PMC9173860/
2. [2] https://www.sciencedirect.com/science/article/pii/S0006349504735341
3. [3] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.6.2 Why is the colour of the clear Sky Blue? > p. 169
4. [4] https://pmc.ncbi.nlm.nih.gov/articles/PMC5357263/